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Study: Tobacco, Not Marijuana Could Be The Big IQ Killer

Guy Bentley

Smoking tobacco might negatively affect teen students’ grades more than marijuana use, according to a new study.

Published in the Journal of Psychopharmacology, researchers examined 2,235 children, investigating their IQ and educational performance from ages 15 to 16. The sample was taken from the Avon Longitudinal Study of Parents and Children.

The effects of marijuana use on teen learning and cognitive abilities has become an even more hot-button issue after October data from the Centers for Disease Control and Prevention (CDC) showed young people were more likely to smoke pot than tobacco. (RELATED: Tipping Point: Marijuana Use Overtakes Tobacco Among High School Students)

Almost a quarter of the subjects reported having tried marijuana at age 15. “After full adjustment, those who had used cannabis 50 times did not differ from never-users on either IQ or educational performance,” said the study’s authors.

“These findings suggest that adolescent cannabis use is not associated with IQ or educational performance once adjustment is made for potential confounds, in particular, adolescent cigarette use. Modest cannabis use in teenagers may have less cognitive impact than epidemiological surveys of older cohorts have previously suggested,” they added.

The findings were substantially different for tobacco use. After adjusting for group differences in cigarette smoking, there was a significant weakening of the relationship between cannabis use, IQ and educational outcomes. But the study did demonstrate “robust associations between cigarette use and educational outcomes, even with cannabis users excluded.”

The research will add strength to arguments made by the likes of the International Centre For Science In Drug Policy (ISCDP), which say marijuana use does not significantly lower IQ.

The oft-made claim that smoking weed can lower IQ scores by as much as eight points has been revised and abandoned, according to the ISCDP. The authors of one of the most frequently-cited papers linking marijuana to falling intelligence revised their data in 2013 and found that socio-economic status was a better explanation for IQ decline. (RELATED: Study: Scientists Bust Marijuana Myths And Tell Politicians To Stop Scaremongering)

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